Method and apparatus for leak testing of pipe

ABSTRACT

A method of testing pipe sections at an oil rig floor by means of an internal pipe testing tool and a pressurized gas containing helium in a ratio of helium to a carrier gas of at least about 1:2856 by volume. The gas is pressurized in a hydraulic accumulator remote from the rig floor. The pressurized gas actuates the test tool at substantially the same pressure as is used for testing the pipe section. A flexible enclosure confines the test gas which leaks from the pipe section. The enclosure defines a substantially annular chamber around the area to be tested to confine leakage test gas to prevent its dissipation into the atmosphere. An aperture is provided in the enclosure to permit a sensing probe to be inserted into the annular chamber between the enclosure and the pipe section to sense the presence of test gas.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending application Ser.No. 458,790, filed Jan. 18, 1983, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to leak testing of pipe sections by means of apressurized test gas, and more particularly to a method and apparatusfor testing for minute leakage at a test section and including anenclosure device for confining any test gas that leaks through the testsection.

The testing of fluid conduits for leak tightness is a commonrequirement, especially in the oil and gas well field. In the oil field,the testing of pipe joints is especially important to prevent leakage ofthe gas or oil out of the pipe and loss into the surrounding groundaround the bore hole. Typically in such applications, a hole is drilledin the earth, and as the depth of the hole increases a well casing, inthe form of a pipe, is inserted behind the drill to define the well boreand to permit the introduction and withdrawal of drilling fluids, aswell as the withdrawal of drilling debris. Several sections of such awell casing when connected together are referred to as a well string,and the string is defined by a series of interconnected pipe sections,the interconnections most often being accomplished by means of aninternally threaded union which engages corresponding external threadsat each of the opposed ends of the pipe sections to be joined.

Testing of such pipe joints for leak tightness has most often beenaccomplished by subjecting the pipe joint to high internal fluidpressures. A suitable pipe testing tool is introduced into the interiorof the pipe, the tool being such that it includes spaced resilientpacking glands which are radially extendable against the interiorsurface of the pipe on opposite sides of the area to be tested tothereby define an annular space into which a pressurized liquid, such aswater, can be introduced. An example of a highly preferred pipe testingtool is shown in U.S. Pat. No. 4,548,069, issued Oct. 22, 1985, entitled"Pipe Testing Tool", and owned by the same assignee, the disclosure ofwhich application is incorporated herein by reference. Alternate toolsare shown in U.S. Pat. No. 3,899,920. Any leakage of water through thejoint can then be visually detected, whereupon suitable correctiveaction can be taken.

In addition to the use of pressurized water, it has become acceptedpractice when testing pipe for deeper wells to employ pressurized gas orgases, especially nitrogen gas, to check pipe joints for leak tightness.This is particularly true for testing leak tightness at pressures inexcess of about 10,000 psi. A similar pipe testing tool is employed tointroduce the pressurized gas to the interior of the pipe (see, forexample, the aforesaid U.S. Pat. No. 4,548,069, and a liquid film isapplied to the outside surfaces of the joint in order to visuallyobserve leaking gas bubbles.

Alternatively, when pressurized nitrogen gas has been used in thetesting tool, a cup-like member was positioned around and under theexterior of the joint section to be tested, and tightly engaged thesection of pipe immediately below the test section to define an externalannular chamber open at the top and closed at the bottom. Water wasplaced in the annular chamber, and a leak site manifested itself by theappearance of nitrogen bubbles rising in the surrounding water, whichcan be visually detected. An example of such a "bubble bucket" is shownin U.S. Pat. No. 3,385,103, issued May 28, 1968, to John F. Wilkerson.

Nitrogen gas has limitations with respect to the size of leak siteswhich can be detected and the speed with which nitrogen gas can disclosethe existence of very small leak passages. As well known in the art, thespeed by which a leak is detected is very important in the oil fieldinasmuch as the time necessary to make the test is lost and cannot berecovered in the drilling operations. Hence, time saved in conductingthe test is time and money saved in drilling the well.

Another method, not used in the oil field, for checking for small leaksin pipe connections involves the use of a pressurized gas, the escape ofwhich is sensed by a suitable sensing probe. The output of the sensingprobe, which will detect minute quantities of the gas, is then displayedon a meter, screen, or the like. However, because of possibledissipation into the atmosphere by air currents, minute amounts ofleakage gas could easily escape detection. A suitable enclosure has beendisclosed to surround the test section and thereby prevent dissipationinto the atmosphere of the test gas which leaks through the joint. Anexample of one form of enclosure to accomplish that purpose is shown anddescribed in U.S. Pat. No. 4,282,743, which issued Aug. 11, 1981, toPatrick T. Pickett. However, the Pickett enclosure is not used inconjunction with an internal tool to introduce the gas and seal off thesection to be tested, and the fitting arrangement disclosed in thePickett patent is a two-piece structure which must be carefullyassembled around the section to be tested and thus is too cumbersome touse in the oil field.

It is therefore desirable to provide an improved method and apparatusfor pressurized testing of oil field pipe using a gas mixture that canpass through extremely small leak sites, which are too small to passpure nitrogen gas, and which can be detected much more rapidly than purenitrogen through leak sites that pass nitrogen but only at a slow rate.

In addition to providing an improved test gas mixture, it is alsodesirable that an improved leak test enclosure and pressurizing systembe provided for use in conjunction with an appropriate internal pipetesting tool, wherein the pressurizing system permits pressurization ofthe test gas to high pressures while minimizing dangerous risks on therig floor previously encountered and the enclosure is more convenient touse and can rapidly be applied to and removed from the pipe connectionto be tested.

SUMMARY OF THE INVENTION

It is the principal object of the present invention to provide animproved apparatus and method of testing pipe sections for leakage usinga test gas mixture that can rapidly pass through extremely small leaksites to permit rapid leak detection.

It is another principal object of the present invention to provide aunique leak test enclosure for use in conjunction with an appropriateinternal pipe testing tool for sensing the leaking gas or the gasmixture

A further object of the present invention is to provide a leak testenclosure which is flexible and removable and can be quickly positionedabout a test section.

Still a further object of the present invention is to provide a leaktest enclosure which is readily positioned about and removed from a pipetest section under test using an appropriate internal pipe testing tool,which can accommodate different size pipe diameters without the need foradjustment, and which completely encloses the pipe section for rapiddetection of leakage gas that is present in the interior of the pipesection being tested.

Yet another object of the present invention is to provide a uniquesystem for pressurizing the test gas mixture in combination with anappropriate internal pipe testing tool whereby the tool is activated andset in the pipe section to be tested at substantially the same pressureas the pressure of the test mixture used in testing the pipe section.

Briefly stated, in accordance with the principal aspect of the presentinvention, a method of testing pipe for leakage is provided wherein atest gas in the form of a gaseous mixture of helium and a carrier gas isintroduced at the test section by an appropriate internal pipe testingtool. The internal pipe testing tool used in the instant inventionrelies upon a single source of high pressure gas both to set the toolinside the pipe section to be tested and to exit the tool and test thepipe section (see U.S. Pat. No. 4,548,069). The test gas must contain adetectable percentage of helium so that its escape through very smallleak sites can be detected. A ratio of helium to carrier gas greaterthan at least about 1:10 by volume has been found preferred. Theinternal tool and pipe section are both pressurized with the test gas tosubstantially the same internal pressure of from about 3000 psi to about20,000 psi and the presence of leakage of the helium gas at the testsection is sensed.

In another aspect of the invention, improved pressurizing apparatus isprovided together with an enclosure for confining adjacent to the testsection the test gas that has leaked through the test section. Theenclosure comprises a unitary, substantially gas impermeable flexiblebody having a pair of spaced open ends defined by resilient,substantially gas impermeable end sealing means to close the ends of thebody portion when the enclosure is assembled in substantiallyfluid-tight engagement with the exterior of the pipe around the sectionto be tested. Closing means carried by the enclosure are provided topermit the body to define a chamber around the test section to confinethe test gas therewithin.

In another embodiment of the invention, the enclosure is provided in theform of a flexible sheet which includes longitudinally spaced stiffenermembers that serve to space the enclosure from the outer periphery ofthe test section and provide a chamber therearound.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing gas pressurization and leak detectionapparatus for testing the leak tightness of pipe joints in accordancewith the present invention.

FIG. 2 is a fragmentary perspective view of a pipe section including oneform of leak test enclosure in accordance with the present invention.

FIG. 3 is a longitudinal cross-sectional view taken along the line 3--3of FIG. 2.

FIG. 4 is a transverse cross-sectional view taken along the line 4--4 ofFIG. 2.

FIG. 5 is a fragmentary perspective view of a pipe joint sectionincluding another form of leak test enclosure in accordance with thepresent invention.

FIG. 6 is a transverse cross-sectional view taken along the line 6--6 ofFIG. 5.

FIG. 7 is a plan view of the enclosure shown in FIG. 5 after the samehas been removed from the pipe and has been fully opened.

FIG. 8 is a fragmentary perspective view of a pipe section showinganother form of leak test enclosure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and particularly to FIG. 1 thereof, thereis shown a section of pipe 10, a portion of which is surrounded by oneform of leak test enclosure 12 in accordance with the present invention.The pipe section includes a joint or union 46 by which two portions ofpipe are joined together. A detection probe 8 is provided to detectleakage of test gas that is fed under pressure into pipe section 10. Theprobe is connected to a gas detector 9 to provide either a visual orother convenient indication of leakage of the test gas from inside thepipe section through the joint and into enclosure 12. One type ofsuitable gas detector that can be used to detect leakage of the test gasis a GOW-MAC Gas Leak Detector, Model No. 21-250, Manufactured byGOW-MAC Instrument Co., Bridgewater, N.J.

The test gas, the composition of which will be described hereinafter inmore detail, is provided from a gas source 1 to an accumulator 2, in theform of a pressure vessel, through a pipe 1a, a remotely controlled gasfill valve 1b, and a check valve 1c. Fill valve 1b can be pneumaticallyor electrically operated from a remote control panel 3 to permit thetest gas to enter the accumulator until pressure equilibrium with thegas source takes place, which can be, for example, at a pressure of fromabout 400 psi to about 1000 psi. Additional pressurization of the gas tothe desired test pressure, which can be of the order of about 10,000 psior more, is obtained by introducing a pressurized liquid, such as water,into the lower portion of accumulator 2 from a water source 4, throughpipe 4a, by means of pump 4b. A check valve 4c is provided to preventbackflow and a manually operated relief valve 4d is provided. Anisolation valve 4e is provided in the event repairs are desired to bemade upstream of valve 4c without relieving the pressure in accumulator2. A relief valve 4f remotely operated from control panel 3 is providedto permit bleed-off of water, and consequent reduction of pressure,after a pressure test has been completed.

After pressurization of the test gas in accumulator 2 to the desiredtest pressure, a gas supply valve 5 is remotely operated from controlpanel 3 to admit pressurized test gas into pipe 6 that is connected withtest tool 7 (see FIG. 3) positioned within the pipe. Any temporaryreduction in pressure is eliminated by pumping more water into theaccumlator. In the form of test tool used in accordance with the presentinvention, only a single source of pressurized gas is fed to the testtool. The pressurized gas sets the seals of the test tool against theinternal wall of the pipe to define the section to be tested. At thesame time, the pressurized gas exits from the tool into the annularspace between the outside of the tool ard inside of the pipe sectionunder test as defined by set seals. As a result, the pressurized gaswhich sets the seals of the test tool and the pressurized gas whichtests the pipe section for leaks are substantially the same pressure.

After the test has been completed, the relief valves 4d and 4f areopened and the compressed gas in the test tool forces the water, orother hydraulic fluid, back out of the accumulator. These valves remainopen until gas starts to escape, after which they are closed. The gassupply valve 5 is also closed, thus trapping most of the gas in theaccumulator. The remote atmosphere gas bleed off valve 5a is then openedto allow any gas trapped between the accumulator and the test tool toescape. It is then closed and the cycle can start again.

By this hydraulic system of pressurization of the test gas, theaccumulator can be located at a position remote from the rig floor andthe control panel. Thus, the control panel can be operated at the rigfloor but the sometimes dangerous accumulator can be located where anyrupture or breakage due to high pressures will not cause any injury.

As shown in FIG. 2, enclosure 12 includes a generally tubular body 14which is split longitudinally to define a pair of opposed longitudinaledges 16, 18. Adjacent each of longitudinal edges 16, 18 is a stiffenerbar 20, 22, respectively, which can be secured thereto by means of bolts24, or the like. Stiffener bars 20, 22 each include one element of alocking bar arrangement, stiffener 20 carrying a notched locking bar 26,and stiffener 22 carrying a notched retainer 28, the arrangement andoperation of which will hereinafter be described in more detail.Positioned circumferentially about the outer periphery of the body andsuitably secured to stiffener bars 20, 22 are a pair of arcuate handlesupports 30, 32, respectively, which extend for approximately 90° of arcin opposite directions around tubular body 14. Extending outwardly fromeach of handle supports 30, 32 is a spreader handle 34, 36,respectively, each of which preferably is positioned on opposite sidesof body 14 to facilitate the separation and spreading of longitudinaledges 16, 18.

Each of the ends of tubular body 14 includes a transversely extending,inwardly directed, resilient seal 38, 40 (only one of which is visiblein FIG. 2), that is adapted to sealingly enage the outer surfaces of thepipe sections 42, 44 which are joined by union 46 (see FIGS. 3 and 4),and provide a seal between the respective pipes adjacent the joint andtubular body 14 to prevent dissipation of any test gas that leaks intothe annular chamber 48 therebetween. Seals 38, 40 are of generallyannular conformation. Flexible seals 50, 52 are positioned along each oflongitudinal edges 16, 18, respectively, to assist in preventing thedissipation of any test gas that leaks into annular chamber 48 Althoughtwo seals 50, 52 are shown, it is not essential that two seals be used,and a single seal secured to either of longitudinal edges 16 or 18 canbe employed, if desired.

The locking means for holding seals 50, 52 in sealing engagement is mostclearly seen in FIG. 4. Notched retainer 28 is positioned onlongitudinal stiffener 22 intermediate the ends thereof. Locking bar 26is pivotally secured to a yoke member 54 which is, in turn, secured tolongitudinal stiffener 20 intermediate the ends thereof. Biasing means,such as spring 56, is provided and bears against locking bar 26outwardly of the pivot 27 to urge the notch thereof toward notchedretainer 28. As can be seen in FIG. 4, locking bar 26 and retainer 28have cooperable notched edges 58, 60, respectively, which are sopositioned relative to each other that longitudinal edges 16, 18,respectively, are held in tight engagement when the locking means isengaged.

As best seen in FIG. 3, a typical pipe joint includes a threaded union46 which engages corresponding external threads on each of adjacent pipesections 42, 44, and defines part of the inner surface of annularchamber 48. Internal test tool 7 is positioned within the pipe adjacentthe joint section to be tested, with upper seal or seals 21 above thejoint and lower seal or seals 23 below. Prior to pressurizing the tool,the outside diameter of the seals 21 and 23 are sufficiently smallerthan the internal diameter of the pipe of allow the tool to traverseeasily therein. Upon pressurization, the seals expand to engage theinternal diameter of the pipe and seal the section to be tested, all asfully described in U.S. Pat. No. 4,548,069.

Also provided in tubular body 14 are a probe aperture 62 through which asuitable sensing probe 8 can be inserted in order to sense the presenceof leakage gas that flows from a defective joint into annular chamber48. Additionally, a small vent aperture 64 can be provided to permit theinflow of a small amount of air to replace the gas sample that iswithdrawn by the sensing probe. Vent aperture 64 prevents the formationof a slight vacuum, which could otherwise develop if the gas withdrawnthrough the sensing probe is not replaced by a corresponding volume ofair.

Tubular body 14 is preferably formed from a substantially gasimpermeable material which is sufficiently flexible to permit theopening of the slot defined by longitudinal edges 16, 18 and at the sametime sufficiently resilient to permit enclosure 12 to assume itsoriginal shape when the spreading force for opening the slot arerelaxed. Suitable materials include flexible sheet metal, or plastics,such as tubular polyurethane, polyvinyl chloride, or the like.

In operation, union 46 is threadedly secured to an end of the pipesection 44, and an end of pipe section 42 is threadedly engaged with theupper portion of union 46 to define a complete joint. Thereupon testenclosure 12 of the present invention is positioned about union 46 byspreading handles 34 and 36 until longitudinal edges 16 and 18 areseparated a distance sufficient to permit the enclosure to be placedover the pipe section. Once enclosure 12 is in position, the spreadingforces on handles 34 and 36 are released, and the resilience of tubularbody 14 causes longitudinal edges 16 and 18 to move close to each other.Closing forces are then applied to spreader handles 34 and 36 to bringedges 16 and 18 together so that seals 50 and 52 are in sealingengagement. The locking means is actuated by continued closing pressureon the spreader handles until a point is reached where the notches 58and 60 on locking bar 26 and notch retainer 28, respectively, areengaged by the action of biasing spring 56. Thereafter the closingforces on spreader handles 34 and 36 are released and the locking meansmaintains the enclosure in a closed condition.

After the enclosure is properly positioned around the joint, theinterior pipe 10 adjacent the joint is pressurized by means of a highpressure test gas. Preferably, the test gas includes at least about 9%by volume helium. If the joint is gas-tight, none of the pressurizedtest gas will leak into annular chamber 48 between the pipe joint andthe enclosure. If a leak exists, then pressurizing gas including atracer (preferably helium) will leak into annular chamber 48 and thesensing probe inserted through probe aperture 62 will detect thepresence of the tracer gas by withdrawing a portion of the gas in theannular space for analysis by a spectrophotometer, or by anothersuitable sensing device capable of detecting and indicating the presenceof the tracer gas. The withdrawn gas sample can be replaced by air whichis permitted to enter the enclosure through vent aperture 64.

Another embodiment of the enclosure is illustrated in FIGS. 5-7,inclusive, which provides another form of enclosure 70 positioned abouta pipe 72 and which functions in a manner similar to the embodiment ofFIGS. 2-4, inclusive. Structurally, however, enclosure 70 is provided asa flexible wrap 74 that is adapted to be wrapped around pipe 72. Wrap 74includes an inner face 76, an outer face 78, and a plurality oflongitudinally spaced, arcuate stiffener members 80 positioned toprovide body to the wrap so that when it is wrapped around a testsection, stiffeners 80 will prevent the complete inward collapse of wrap74 and will cause substantial inner portions thereof to be spaced fromthe outer periphery of pipe 72 a sufficient distance to define anenclosed chamber into which a sensing probe (not shown) can be inserted.Although shown in FIGS. 5 and 6 as positioned between inner face 76 andouter face 78, stiffeners 80 can also be positioned directly on eitherof those faces, if desired, so long as they are capable of spacing aportion of the wrap from the outer surface of pipe 72.

As shown in FIG. 7, wrap 74 is of generally rectangular configuration,with the major dimension thereof arranged around the outer surface ofpipe 72 as shown in FIG. 5. A pair of resilient longitudinal seals 82,which can be solid or foamed rubber or plastics, is positioned at innersurface 76 parallel to and spaced inwardly of the longer edges of wrap74, and similar seals 84 are positioned along the shorter edges thereofon both faces of the wrap to permit either shorter edge thereof tooverlie the other when the wrap is installed for use.

Positioned along each of the longer edges and outwardly of each of seals82 is a separable connecting means to permit removable engagement ofportions of the longitudinal edges when the same are in overlappedcondition. A suitable connecting means is a pair of cooperating strips86 of material known as "Velcro" which on one surface consists of aseries of loop-type elements, and on the opposed, engaging surface itincludes a plurality of outwardly extending, hook-like elements. Similarseparable connecting means 87 are provided at the edges of the wrap.

Also positioned on flexible wrap 74 and preferably at one pair ofadjacent corners thereof are tabs 88 to provide a gripping means tofacilitate the installation of the device around pipe 72 and to permitthe respective longitudinal edges thereof to be drawn into tightengagement with the pipe outer surface to prevent dissipation of testgas by wind or other external air currents.

Suitable sheet materials for forming the flexible wrap are plastic filmsor other substantially gas impermeable materials, a pair of which can besealed or otherwise joined along their marginal edges to provide innerface 76 and outer face 78 and within which stiffener members 80 can bepositioned. A suitable plastic film is polyvinyl chloride. Stiffeners80, which are of curved shape, are preferably positioned inlongitudinally spaced relationship along wrap 74 and can be formed fromany rigid yet resilient materials, such as sections of plastic tubinghaving sufficient thickness to provide rigidity. The several stiffenerscan be retained in spaced pockets (not shown) formed between the innerand outer faces of the wrap. Additionally, stiffeners 80 can also besecured to the inner or outer faces of wrap 74, if desired.

The wrap of FIG. 7 is shown installed for use on a section of pipe inFIGS. 5 and 6, wherein the longitudinal edges are shown to be inperipheral contact with the outer surface of pipe 72. As in theembodiment of FIGS. 2 to 4, a sensing probe aperture 90 is provided andcan be in the form of a tubular member 90 which extends from theinterior surface of the wrap 74 to an outer longitudinal edge in orderto provide an entry passageway for a sensing probe. If desired, asimilarly configured tubular vent aperture (not shown) can also beprovided, for example, on the opposite edge of wrap 74 from tubularmember 90, to permit a small amount of air to enter the enclosure andreplace the gas volume withdrawn by the sensing probe, therebypreventing the pressure within the enclosure from dropping below theatmospheric pressure.

Another form of test enclosure is illustrated in FIG. 8. As there showna pair of resilient, split enclosure halves 101, 102 are secured to andcarried by a pair of steel outer casings 103, 104. The enclosure halves101, 102 function in a manner similar to the embodiments of FIGS. 2-4and include a probe aperture 105. The steel outer casings provideincreased safety for those in the vicinity of the test enclosure bylaterally containing any fragments or high gas pressures that mightoccur in the event of rupture or other failure at the joint. Lockingmeans similar to that illustrated in FIG. 4 can be provided on casings103, 104 to securely lock them together.

Thus it can be seen that the leak test enclosure herein describedprovides a rapid and secure means for enclosing a test section forconfining leakage of tracer gas utilized to test for joint leakage. Thedevice does not involve the necessity for using water for detecting gasbubbles, and therefore it is usable in even the coldest weather, whenfreezing of water would be a problem. It also eliminates the need toperiodically replenish any water which may have been lost as a result ofaxial movement, relative to the pipe sections, of the previously-usedbubble bucket over various enlarged areas of pipe, which can causedeflection of the bucket lower seal with consequent loss of water.

As part of the present invention, it has been discovered that helium, asthe tracer or test gas, either alone or in combination with anotherinert gas or gases, such as nitrogen, in a gas mixture containing acritical minimum level of helium, produces unexpected results indetecting previously undetectable, very small leak passages in oil fieldpipe, and reduces the test time for detecting somewhat larger leakpassages than previously possible with prior known pressurized gassystems. Without intending to be limited, it is believed that helium issuperior to prior pressurized gas systems, particularly nitrogen used inthe prior systems, for the following reasons. Methane is the principalconstituent of subterranean gas, which is under high pressure within thedrill string. Nitrogen has a higher molecular weight and, therefore, ahigher mass than methane. Thus, when nitrogen is used as the test gasfor detecting leaks in a drill pipe section, the nitrogen cannot escapefrom very small leak passages that might otherwise allow methane toescape, and it will flow through very small but passable leak sites at aslower rate than methane. On the other hand, helium has a lowermolecular weight and, therefore, a lower mass than methane, and muchlower than nitrogen. Thus, it is hypothesized that helium can detectvery small leak passages, smaller than those detectable by nitrogen gas,and can detect small but passable leak sites at a more rapid rate thannitrogen, because its molecular size is smaller than methane, and muchsmaller than nitrogen. In other words, because helium has a lowermolecular weight and, therefore, a lower mass than does methane, heliumshould be capable of detecting all leak sites which might passsubterranean gas (essentially methane), even leak sites that would notpass nitrogen, as well as more rapidly detecting somewhat larger leaksites which are capable of passing nitrogen, but only at a slow rate.Other gases which have similar molecular weight and mass characteristicsas helium with respect to methane could be used in the presentinvention, such as hydrogen and oxygen, if they were not otherwiseobjectionable. However, neither hydrogen nor oxygen can be used inaccordance with the present invention because of their combustibility inthe environment in which the present invention is used. Helium gaspossesses all of the necessary qualities for carrying out the presentinvention. Other gases that are also suitable include: ethane (3.0%),methane (5.0%), monochloromethane, fluorotrichloromethane,dichlorodifluoromethane, chlorotrifluoromethane,dichloromonobromomethane, monochlorodifluoromethane, sulfurhexafluoride, and propane (2.1%), among others, the parenthetical weightpercentages given reflecting approximate maximum concentrations for safeoperation.

Tests using a GOW-MAC Model No. 21-250 gas leak detector to measure leakrates through a given leak site have shown that the leak rate for heliumis approximately 2.6 times that for nitrogen. Table I below presents theleakage rates which correspond with a given reading on a GOW-MACdetector for a given leak site:

                  TABLE I                                                         ______________________________________                                        Helium Leak Rate Comparison to Nitrogen Leak Rate                             and Its Detection Using a GOW-MAC Detector                                                   Divisions of                                                                  Deflection on                                                                 GOW-MAC                                                        Helium Leak Rate                                                                             Detector   Nitrogen Leak Rate                                  (cm.sup.3 /sec)                                                                         (ppm)*   (metal units)                                                                            (cm.sup.3 /sec)                                                                        (ppm)*                                 ______________________________________                                        1.1 × 10.sup.-5                                                                   10       10         0.41 × 10.sup.-5                                                                  3.8                                   2.2 × 10.sup.-5                                                                   20       20         0.83 × 10.sup.-5                                                                  7.6                                   3.3 × 10.sup.-5                                                                   30       30         1.3 × 10.sup.-5                                                                  11.3                                   4.4 × 10.sup.-5                                                                   40       40         1.7 × 10.sup.-5                                                                  15.0                                   5.5 × 10.sup.-5                                                                   50       50         2.1 × 10.sup.-5                                                                  19.0                                   6.6 × 10.sup.-5                                                                   60       60         2.5 × 10.sup.-5                                                                  22.6                                   7.7 × 10.sup.-5                                                                   70       70         2.9 × 10.sup.-5                                                                  26.4                                   8.8 × 10.sup.-5                                                                   80       80         3.3 × 10.sup.-5                                                                  30.2                                   9.9 × 10.sup.-5                                                                   90       90         3.7 × 10.sup.- 5                                                                 34.0                                   11.0 × 10.sup.-5                                                                  100      100        4.2 × 10.sup.-5                                                                  38.0                                   55.0 × 10.sup.-5                                                                  500      500        21.0 × 10.sup.-5                                                                 190                                    110.0 × 10.sup.-5                                                                 1000     1000       42.0 × 10.sup.-5                                                                 380                                    ______________________________________                                         *ppm = parts per million                                                 

It has been found that the speed of leak detection is related to thequantity of helium in a given volume of test gas, the greater the volumeof helium, the quicker the response. And it has also been found that aprticular range of mixture ratios of helium to, say, nitrogen, providesas quick a response in terms of identifying a leak site, as pure heliumalone, thereby permitting such tests to be performed using a smalleramount of helium.

Specifically, tests were performed using a known leakage area andsubjecting it to a test gas at a given pressure to provide a constantleak rate of the test gas through the leak site. The test gas was amixture of helium and nitrogen. The ratio of helium to nitrogen wasvaried and the time for the detector to achieve the maximum reading wasmeasured. The results of that test are presented in Table II below:

                  TABLE II                                                        ______________________________________                                                                        Detection                                     Helium to Nitrogen     Test     Time in sec                                   Ratio       Leak Rate  Pressure for maximum                                   (By volume) (cm.sup.3 /sec)                                                                          (psi)    reading                                       ______________________________________                                        100% Helium 1.2 × 10.sup.-5                                                                    5,800    8                                             1:1         1.2 × 10.sup.-5                                                                    5,800    8                                             1:2         1.2 × 10.sup.-5                                                                    5,800    8                                             1:3         1.2 × 10.sup.-5                                                                    5,800    8                                             1:4         1.2 × 10.sup.-5                                                                    5,800    8                                             1:5         1.2 × 10.sup.-5                                                                    5,800    8                                             1:8         1.2 × 10.sup.-5                                                                    5,800    8                                             1:9         1.2 × 10.sup.-5                                                                    5,800    10                                             1:10       1.2 × 10.sup.-5                                                                    5,800    11                                             1:12       1.2 × 10.sup.-5                                                                    5,800    11                                             1:14       1.2 × 10.sup.-5                                                                    5,800    12                                            ______________________________________                                    

From the results presented in Table II above, it can be seen that heliumto nitrogen ratios of as low as 1 part helium to 8 parts nitrogen, byvolume, result in the same detection time to achieve a maximum readingon the gas detector. Ratios of 1:9 or less resulted in increaseddetection times to achieve the maximum reading. Additionally, in usingthe test gas mixtures as given above, it is preferred that the testpressure be from about 3000 psi to about 20,000 psi in order to assuredetecting even the smallest leak sites within a reasonable time period,

If the time involved to detect a leak is not a critical factor, test gashaving even smaller concentrations of helium can be used. The followingtests were conducted to permit a determination of the minimum quantityof helium in the test gas to permit a leak to be detected using theGOW-MAC instrument.

A GOW-MAC gas leak detector (Model #21-250), which detects gases basedupon their thermal conductivity as compared with that of air, and aConsolidated Electrodynamics helium mass spectrometer were used todetermine the minimum helium to nitrogen operating mixtures which couldbe detected at a fixed pressure and leak rate. The minimum absolutehelium leak rate detectable by the GOW-MAC Unit and the ConsolidatedElectrodynamics Unit (sold by Du Pont, and henceforth referred to as theDu Pont unit) was also determined.

In performing the testing, helium and nitrogen mixtures of knownconcentrations were pressurized up to 5500 psig and a test section ofpipe was filled with the test gas mixture at that pressure. An enclosureof the type hereinbefore described was placed around the leaking testsection and readings were taken from the GOW-MAC tester 30 seconds and60 seconds after placing the enclosure around the test section. Thissame procedure was repeated for the Du Pont unit. A fixed leak rate wasset with a test gas mixture in which helium was present in an amount of6.67% by weight with the balance being nitrogen. The leak rate was setso that with that concentration of helium the GOW-MAC unit displayed ascale reading of 3000 after 30 seconds. The same leak rate was usedthroughout the testing.

Gas mixtures of 6.7% helium and 93.3% nitrogen, by weight; 0.10% heliumand 99.90% nitrogen, by weight; 0.020% helium and 99.980% nitrogen, byweight; and 0.0050% helium and 99.9950% nitrogen, by weight, were usedin the tests. A calibration gas mixture including 6.65×10⁻⁷ cc-atm/secof helium was used to calibrate the Du Pont unit in order to permit adetermination of the rate of helium leakage. The following equation wasused to calculate the absolute helium leak rate using the Du Pont unit:Absolute helium leak rate=sensitivity of the unit X reading on themeter. The sensitivity of the Du Pont unit was determined duringcalibration. The meter was read at 30 seconds into the test. For a testmixture to be considered detectable, a minimum signal to noise ratio of4 was selected, which means that the meter on each instrument must read4 times the noise reading at maximum sensitivity in order for a leak tobe considered detectable. The noise reading of each unit at maximumsensitivity was 5, so that the minimum reading on each unit fordetecting a leak was 20.

The following parameters were used consistently throughout the testing:

    ______________________________________                                        Pressure in the test section                                                                       5500 psig                                                Temperature of pressurized gas                                                                     77° F. (ambient)                                  Test enclosure       The embodiment of                                                             FIG. 2                                                   Maximum noise (each unit)                                                                          Reading of 5 at                                                               maximum sensitivity                                      Minimum signal to noise ratio                                                                      4                                                        for determining a leak                                                        Times readings were taken                                                                          30 seconds and 60                                                             seconds                                                  ______________________________________                                    

    ______________________________________                                        DU PONT UNIT                                                                  ______________________________________                                        Operating Pressure                                                                              0.15 microns                                                Accelerating Current                                                                            60%                                                         Ionization Current                                                                              50%                                                         Calibration Mixture                                                                             6.56 × 10.sup.-7 cc-atm/sec                                             helium                                                      Sensitivity       As stated in each test                                                        (checked during each test)                                  ______________________________________                                         NOTE:                                                                         A sniffer tube was used on the Du Pont unit throughout testing.          

The following tests were conducted:

    ______________________________________                                        TEST #1                                                                       Gas Mixture   6.7 wt. % helium (33.3 mol %)                                                 93.3 wt. % nitrogen (66.7 mol %)                                Sensitivity of the                                                                          2.73 × 10.sup.-10 cc-atm/sec helium                       Du Pont Instrument                                                                          Time         Reading                                            GOW-MAC Readings                                                                            30 sec.       3000                                                            60 sec.       5000                                              Du Pont Readings                                                                            30 sec.      11000                                                            60 sec.      23500                                              Absolute Helium Leak                                                                        3.00 × 10.sup.-6 cc-atm/sec                               Rate                                                                          ______________________________________                                        TEST #2                                                                       Gas Mixture   0.10 wt. % helium, (0.70 mol %)                                               99.90 wt. % nitrogen, (99.30 mol %)                             Sensitivity of the                                                                          2.73 × 10.sup.-10  cc-atm/sec helium                      Du Pont Instrument                                                                          Time         Reading                                            GOW-MAC Readings                                                                            30 sec.        22                                                             60 sec.        38                                               Du Pont Readings                                                                            30 sec.       5300                                                            60 sec.      11000                                              Absolute Helium Leak                                                                        1.16 × 10.sup.-6 cc-atm/sec                               Rate                                                                          ______________________________________                                        TEST #3                                                                       Gas Mixture   0.020 wt. % helium, (0.14 mol %)                                              99.980 wt. % nitrogen, (99.86 mol %)                            Sensitivity of the                                                                          1.64 × 10.sup.-10 cc-atm/sec helium                       Du Pont Unit                                                                                Time         Reading                                            GOW-MAC Readings                                                                            30 sec.        0                                                              60 sec.        0                                                Du Pont Readings                                                                            30 sec.        60                                                             60 sec.       500                                               Absolute Helium Leak                                                                        1.64 × 10.sup.-8 cc-atm/sec helium                        Rate                                                                          ______________________________________                                        TEST #4                                                                       Gas Mixture   0.0050 wt. % helium, (0.035 mol %)                                            99.950 wt. % nitrogen, (99.965 mol %)                           Sensitivity of the                                                                          2.20 × 10.sup.-10 cc-atm/sec.                             Du Pont Unit                                                                  GOW-MAC Readings                                                                            NONE                                                                          Time         Reading                                            Du Pont Readings                                                                            30 sec.        21                                                             60 sec.       321                                               Absolute Helium Leak                                                                        4.62 × 10.sup.-9 cc-atm/sec helium                        Rate                                                                          ______________________________________                                    

The GOW-MAC unit displayed a reading after 30 seconds in Test #2 of 22.This is 10% above the minimum reading for accurately detecting a leakusing that instrument and thus the Test #2 gas mixture (0.10 wt. %helium-99 wt. % nitrogen, 0.70 mol % helium-99.30 mol % nitrogen) is thelowest helium to nitrogen mixture accurately detectable by the GOW-MACunit. The extra 10% provides a further safety factor. The minimumdetectable helium leak rate under the Test #2 conditions is 1.16×10⁻⁶cc-atm/sec helium.

Test #4 gives the minimum helium to nitrogen mixture usable with the DuPont unit and after 30 seconds of leaking, the instrument displayed areading of 21. This is 5% over the minimum reading for a leak and isconsidered a further safety factor. Hence a mixture of 0.0050 wt. %helium-99.9950 wt. % nitrogen (0.035 mol % helium-99.965 mol % nitrogen)is considered the minimum helium to nitrogen mixture accuratelydetectable under operating conditions using the Du Pont unit. Theminimum detectable helium leak rate under the Test #4 conditions is4.62×10⁻⁹ cc-atm/sec helium. Thus, on a volumetric basis, the minimumhelium to nitrogen ratio for accurate leak detection using the GOW-MACunit is 1:142, while that using the Du Pont unit is 1:2856.

While particular embodiments of the present invention have beenillustrated and described, it will be apparent to those skilled in theart that various changes and modifications can be made without departingfrom the spirit and scope of the invention, and it is intended toencompass within the appended claims all such changes and modificationsthat fall within the scope of the present invention.

What is claimed is:
 1. A method of testing for leaks in oil field pipeat a rig floor by using a single source of pressurized test gas toactuate a testing tool positioned at a pipe test section and topressurize the pipe test section to test for leaks, said methodcomprising:(a) pressurizing a test gas comprising a mixture of adetectable quantity of helium tracer gas and a carrier gas in a rationof helium tracer gas to carrier gas greater than 1:9 by volume to apressure of at least 3000 psi to provide said single source ofpressurized test gas; (b) enclosing an area around the outside of thepipe to define a chamber around the pipe test section to confine a testgas therewithin; (c) actuating the test tool by introducing saidpressurized test gas having a ratio of helium tracer gas to carrier gasgreater than 1:9 by volume and at a pressure of at least 3000 psi fromsaid single source of pressurized test gas into the test tool to sealoff an internal section of pipe to form a closed volume pipe testsection; (d) introducing said pressurized test gas from said singlesource of pressurized test gas at substantially the same ratio of heliumtracer gas to carrier gas greater than 1:9 by volume and atsubstantially the same pressure of at least about 3000 psi as sued toactuate said test tool into said pipe test section; and (e) sensing thepresence of leaking helium tracer gas in the chamber around the outsideof the pipe test section with a sensing means.
 2. The method of claim 1wherein the carrier gas is nitrogen.
 3. The method of claim 1 whereinthe test section is a pipe joint.
 4. The method of claim 1 wherein thetest gas is pressurized to its test pressure away from the rig floor byintroducing a liquid under pressure into a remote tank containing thetest gas.
 5. The method of claim 1 wherein the ratio of helium tocarrier gas in said test gas is greater than about 1:8 by volume.
 6. Anapparatus for testing for leaks in oil field pipe at a rig floor byusing a single source of pressurized test gas to actuate a testing toolpositioned at a pipe test section and to pressurize the pipe testsection to test for leaks, said apparatus comprising:(a) means forpressurizing a test gas comprising a mixture of a detectable quantity ofhelium tracer gas and a carrier gas in a ratio of helium tracer gas tocarrier gas greater than 1:9 by volume to a pressure of at least 3000psi to provide said single source of pressurized test gas; (b) means forenclosing an area around the outside of the pipe to define a chamberaround the pipe test section to confine a test gas therewithin; (c)means for actuating the test tool bv introducing said pressurized testgas having a ratio of helium tracer gas to carrier gas greater than 1:9by volume and at a pressure of at least 3000 psi from said single sourceof pressurized test gas into the test tool to seal off an internalsection of pipe to form a closed volume pipe test section; (d) means forintroducing said pressurized test gas from said single source ofpressurized test gas at substantially the same ratio of helium tracergas to carrier gas greater than 1:9 by volume and at substantially thesame pressure of at least about 3000 psi as used to actuate said testtool into said pipe test section; and (e) means for sensing the presenceof leaking helium tracer gas in the chamber around the outside of thepipe test section with a sensing means.
 7. An apparatus for testing forleaks in oil field pipe at a rig floor by using a single source ofpressurized test gas to actuate a testing tool positioned at a pipe testsection and to pressurize the pipe test section to test for leaks, saidapparatus comprising:(a) an accumulator; (b) means for introducing atest gas comprising a mixture of helium and a carrier gas in a ratio ofhelium to carrier gas greater than 1:9 by volume into said accumulator;(c) pressurization means including means to introduce liquid underpressure into said accumulator to pressurize said test gas to a pressureof at least about 3000 psi to provide said single source of pressurizedtest gas; (d) means for remotely controlling the introduction of testgas and liquid into said accumulator and for controlling the flow ofpressurized test gas from said accumulator; (e) means for enclosing anarea around the outside of the pipe to define a chamber around the pipetest section to confine a test gas therewithin; (f) means for actuatingthe test tool by introducing said pressurized test gas at a pressure ofat least 3000 psi from said single source of pressurized test gas intothe test tool to seal off an internal section of pipe to form a closedvolume pipe test section; (g) means for introducing said pressurizedtest gas from said single source of pressurized test gas atsubstantially the same pressure of at least about 3000 psi as used toactuate said test tool into said pipe test section; and (h) means forsensing the presence of leaking helium tracer gas in the chamber aroundthe outside of the pipe test section with a sensing means.
 8. A methodof testing for leaks in oil field pipe at a rig floor by using a singlesource of pressurized test gas to actuate a testing tool positioned at apipe test section and to pressurize the pipe test section to test forleaks, said method comprising:(a) introducing a test gas comprising amixture of helium and a carrier gas in a ratio of helium to carrier gasgreater than 1:9 by volume into an accumulator; (b) pressurizing thetest gas in the accumulator by introducing liquid under pressure intothe accumulator to pressurize the test gas to a specified pressure of atleast about 3000 psi to provide said single source of pressurized testgas; (c) remotely controlling the introduction of test gas and liquidinto the accumulator and remotely controlling the flow of pressurizedtest gas from the accmulator; (d) enclosing an area around the outsideof the pipe to define a chamber around the pipe test section to confinea test gas therewithin; (e) actuating the test tool by introducing saidpressurized test gas at a pressure of at least 3000 psi from said singlesource of pressurized test gas into the test tool to seal off aninternal section of pipe to form a closed volume pipe test section; (f)introducing said pressurized test gas from said single source ofpressurized test gas at substantially the same pressure of at leastabout 3000 psi as used to actuate said test tool into said pipe testsection; and (g) sensing the presence of leaking helium tracer gas inthe chamber around the outside of the pipe test section with a sensingmeans.